In response to environmental stresses as well as biological stresses induced by pathogens, insects, viruses and so on, most living organisms, including plants, convert oxygen to reactive oxygen species such as superoxide anion radical, hydrogen peroxide, and hydroxyl radical. Superoxide anion radical (.O.sub.2) is generated from the reaction of molecular oxygen with a free electron. In the presence of iron, hydrogen peroxide is converted to hydroxyl radical (.OH), the most toxic reactive oxygen species. These reactive oxygen species are so reactive that they cause serious physiological damage to organisms.
To eliminate reactive oxygen species, living organisms have various antioxidant systems, which include macromolecular antioxidant enzymes such as SODs, peroxidases, catalases and so on, and other antioxidant molecules such as vitamin C, vitamin E, glutathione and so on. SODs are ubiquitous enzymes converting superoxide anion radical to hydrogen peroxide. To prevent the formation of hydroxyl radical, either peroxidases or calatases scavenge hydrogen peroxide, converting it to water. Thus, SODs play important roles in the antioxidant system and defense mechanism of living organisms, scavenging superoxide anion radical and preventing the formation of hydroxyl radical.
Since SODs are important factors improving tolerance in organisms to environmental stresses, there is a desire to introduce SOD as an ingredient of medicines, foods, cosmetics, and the like. In addition, transgenic plants into which SOD gene is transferred have been produced in order to develop plants tolerant to various environmental stresses, such as ozone, low temperature, herbicides and so on (Plant Physiol., 10, 1049-1054, 1995; U.S. Pat. No. 5,538,878).
It has been reported that SOD is effective on arthritis, rheumatism, ischemic heart disease, radiation hazard and the like. It has been recently revealed that, when applied to UV-irradiated skin, SOD causes recovery of the damaged skin (Experimental Dermatology, 6, 116-121, 1997). These advances have led to the development of medicines which comprise SOD as an active ingredient by pharmaceutical companies in America, Japan, and so on. Additionally, SOD-containing cosmetics to prevent aging of skin have been developed and commercialized in Korea (SOD and active oxygen modulators: pharmacology and clinical trials, NIHON-IGAKUKAN, 1989).
However, because purified SOD loses its activity quickly, there has been an obstacle to the production of medicines or cosmetics in which SOD activity is maintained.